Say all you will about Iron Man 2, which was a pale specter of the first film, but the scene where Downey is trying to find his father's hidden mystery, the one his father couldn't build because the tech didn't exist yet so he hid it in plain sight, illustrates something essential about Tony Stark.

The scene where Downey is trying to figure out the puzzle, where you can see him struggling, if you're a geek of the mathematical persuasion you can feel along with him as the microneural circuits exploit their own plasticity and grow in new directions. The eye-rolling, distant look, the hand scrubbed over the face to create highly localizing distracting stimuli because you desperately know you need or it something inside your head is going to break, Downey captured that high-functioning ADHD/Asperger's look gorgeously.